This invention relates to pipe couplings comprising coupling sleeves for coupling together lengths of pipe in substantially sealed relationship.
The invention is primarily, though not exclusively, concerned with a coupling sleeve for coupling together two lengths of pipe of the type used in sewers, drains and cable conduits, such pipes generally being clay-ware pipes though they may also be of synthetic plastics material.
In the coupling of a pipe in a coupling sleeve, a resilient seal is usually provided so as to prevent liquid material, which passes through the pipe, from escaping to externally of the pipe in the region of the coupling of the pipe to the coupling sleeve and/or in the region of the junction (in the coupling sleeve) between the end of the pipe and the end of a further pipe received in the coupling sleeve.
It is known to provide a seal arrangement, for sealing the entrance of a pipe into a coupling sleeve, and taking the form of a resilient annular seal which is located at one end of the coupling sleeve, and is retained in position by means of a locking ring snap-fitted onto the end of the sleeve. Thus, the seal is shaped to receive the end of the sleeve, and also in turn is received by the locking ring. The seal has a radially inwardly projecting rib which is engaged by a pipe when entered into the sleeve, the rib deflecting part-axially so as to permit entry of the pipe and yet, by the resilience of the seal, maintaining diametric sealing pressure between the coupling sleeve and the external surface of the pipe.
This known arrangement suffers from disadvantages. It is a time consuming and costly task to assemble the arrangement (which is usually carried out by manual/machine manipulation), with evident disadvantage whether the assembly is carried out on the factory floor or on site. Further, the assembly does not always guarantee satisfactory sealing in the event that a pipe is presented which differs substantially from the "norm" shape of pipe which the coupling sleeve is designed to operate with. It is a common experience that pipes, particularly clay-ware pipes, may be ovalised to a certain extent. Evidently, this will give rise to less satisfactory peripheral seal regions where the pipe radius is less than the norm. In such event, liquid can leak round the back of the seal (with respect to the entry direction of the pipe), and may ultimately leak between the inside surface of the seal and the adjacent surface of the end of the coupling sleeve.